In many automated production operations, the products, or other objects, are transported by means of conveyor belt systems. The manufacturer has a large number of inspection systems available for the quality assurance of products, such as for example checkweighers, metal detectors, optical inspection systems, x-ray inspection systems and so forth.
In the production of pharmaceutical or cosmetic products, foodstuffs, beverages and also in the logistics industry, chemical industry, automotive supply industry, and the metal-processing industry, checkweighers are a key element of quality assurance. They improve not only the utilisation of existing resources, but also assist in complying with national regulations, calibration regulations and industrial standards. An effective checkweigher system offers protection against product defects and reduces overall operating costs.
A dynamic checkweigher is a system which weighs products to be weighed while they are conveyed over the scales within the production line, classifies the products to be weighed into predetermined weight zones and sorts or rejects products to be weighed according to the weight classification. Areas in which checkweighers are used are diverse and include for example:
testing for underweight or overweight products;
complying with statutory regulations for the net contents of packaged goods;
reducing product waste by using the weight values obtained by means of the checkweigher to adjust the filling machines;
classifying products according to weight;
measuring and recording the output of production plant or production line; and
verifying piece numbers on the basis of the weight.
All of the products of a production line are weighed with checkweighers. The total product data are thus collected for product counting, batch monitoring or for production statistics.
A checkweigher system usually comprises an infeed belt, a weighing belt, an outfeed belt with a sorting arrangement and a weighing terminal with an operator interface. The weighing belt lying between the infeed belt and outfeed belt is mounted on a weighing cell, which detects dynamically the weight of the product as it travels over the weighing belt. The two most frequently used weighing technologies for checkweighers are weighing cells with strain gauges (DMS) or weighing cells operating accordance to the principle of electromagnetic force compensation (EMFR). After their transport over the weighing belt, the products are carried away by an outfeed belt located downstream of the weighing belt. By means of the dynamic weighing, products having the incorrect weight are detected and ejected by a rejection device usually at right angles to the transport of the products taking place in the longitudinal direction.
Just like checkweighers, metal detectors also belong to the key components for effective quality assurance. Metal detectors are used industrially to search for product impurities, for example for lead pellets in meat, pieces of wire in cereals, shavings due to repairs to the production plant or other impurities from the product processing.
An industrial metal detection system is a highly developed device, with which metallic foreign bodies can be detected and separated out. The detection capability includes ferrous metals, also special steels and non-ferrous metals, such as brass, copper, aluminium and lead. A typical metal detection system comprises at least the following four main components: a seeker head, a transport system, an operating unit and an automatic rejection system. The seeker head usually comprises a plurality of electromagnetic coils, which are each used to generate or detect high-frequency electromagnetic fields.
In order that the metal detector is not disturbed by electrical signals from metallic components or machines in close proximity, the seeker head is accommodated in a shielded manner in a metal housing, usually made of steel or aluminium. The metal housing also serves to improve the strength and rigidity and thus has a significant share in the detection performance of the overall metal detector. The products to be examined are passed, in the case of a plurality of metal detectors, through an opening in the metal housing through the coils of the metal detector.
Despite shielding by means of a metal housing, a part of the high-frequency magnetic field exits to the exterior through the metal detector opening and can impair the performance of the metal detector if this magnetic field is then disturbed by metal objects. In order to achieve optimum metal detection, no metal objects must be present in a certain region around the metal detector opening. This region is referred to as a metal-free zone MFZ. This factor should be taken into account for a reliable detection of the products.
Optical inspection systems are capable of detecting products with a defective appearance dynamically during transport. With cameras and/or scanners, they detect a product as a whole and compare the acquired images on the basis of a reference image (bitmap comparison) and/or on the basis of CAD data (vector comparison). If for example a product displays damage or non-uniformity of the packaging and/or labels applied slanting, it can then be rejected following the inspection system. Such an inspection system is provided at the side of and/or above the conveyor belt and can be shielded by a surrounding housing against interfering influences, such as for example changing lighting conditions.
A frame for a checkweigher is known from DE 103 57 982 A1, with a longitudinal part of the frame extending in the longitudinal direction and intended as a carrying element. The latter can be designed rigid and torsion-proof in such a way that the stability required for the given case of application is achieved. Fitted at both ends of the longitudinal are part flat, plate-like transverse parts, which serve to support the frame on the floor. By designing the longitudinal part as a tube, the risk of contamination remaining on horizontal surface areas of the frame essentially no longer exists. In particular, no fluids remain, but rather run off to the floor. However, the longitudinal part gives rise to a large outlay on material, which also increases the total weight of the frame. In addition, a modular extension of the frame cannot be achieved without quite considerable expense.
Published application WO 2011/064088 A1 proposes a weighing-conveying arrangement, which comprises assembly elements made of plate-like material and transverse struts which connect the adjacent assembly elements, wherein the weighing-conveying arrangement is held on the assembly elements. The assembly elements each comprise a foot region, via which they are assembled on a base, and a holding region at which the weighing-conveying arrangement is held laterally. As a result of the lateral holding of the weighing-conveying arrangement, a moment is introduced into the assembly elements, which leads to a rotation around an axis running parallel in the conveying direction. During the infeed and outfeed of the products to be weighed or checked, the weighing-conveying arrangement can thus be caused to vibrate, which in turn creates poor conditions for the checkweigher used in the weighing-conveying arrangement.
Further frames known from the prior art represent expensive welded structures comprising metal struts extending in the longitudinal direction and transversely thereto. They are in need of improvement with regard to the stability required for the prevention of vibration. Furthermore, they are susceptible to soiling and difficult to clean. These frames likewise cannot be upgraded or extended in an easy manner.
The problem underlying the invention is to provide a frame of the type mentioned at the outset, which requires a reduced structural outlay and at the same time exhibits a high degree of stability, is less susceptible to soiling and easy to clean. The invention is also intended to provide a frame on which the fixing of components and additional equipment can be carried out in a straightforward and rapid manner.
In addition, it should be possible to assemble the frame in a modular design, i.e. the frame should be able to be adapted specifically to the place of operation and to the components to be carried with standardised individual components and/or groups of parts.